How to optimize your Flutter FutureBuilder: Prevent unnecessary rebuilds

Introduction to Flutter and FutureBuilder: A Guide to Avoid Unnecessary Rebuilds

Flutter has made its mark as a powerful framework for mobile application development, enabling developers to create high-quality Android and iOS apps swiftly. This guide will focus on the efficient utilization of the FutureBuilder widget in Flutter to avoid unnecessary rebuilds.

FutureBuilder is a remarkable Flutter widget that handles asynchronous tasks using Future objects. However, even this efficient tool can sometimes lead to unnecessary rebuilds, negatively affecting your application's performance.

In this guide, we will explain how to avoid these unnecessary rebuilds in the FutureBuilder widget. Real-life examples will be used throughout the following sections to simplify these concepts:

- Understanding the Reasons for Unnecessary Rebuilds in FutureBuilder
- Techniques to Avoid Unnecessary Rebuilds in FutureBuilder
- Practical Application of Techniques with Real-Life Examples

Understanding the Reasons for Unnecessary Rebuilds in FutureBuilder

Several reasons contribute to unnecessary rebuilds when using Flutter's FutureBuilder widget. These include:

1. Creation of a Future object within the build method

When a Future object is generated within the build method, FutureBuilder creates a new Future object every time the screen is redrawn. This leads to unnecessary rebuilds and a performance drop in your application.

FutureBuilder(
  future: getData(),
  ...
)

2. Unchanged state leading to continuous recreation of FutureBuilder

Even if the state of the FutureBuilder remains unchanged, the app can continuously recreate FutureBuilder each time it is redrawn, causing performance issues.

3. Non-updating state of StatefulWidget

If FutureBuilder is used within a StatefulWidget and the state does not update, the build method executes again, causing the FutureBuilder to be unnecessarily recreated and potentially decreasing the app's performance.

Understanding these causes will help you identify the right solutions. The next section will delve into ways to address these issues.

Techniques to Avoid Unnecessary Rebuilds in FutureBuilder

To mitigate unnecessary rebuilds, you can apply solutions corresponding to each cause:

1. Position the Future object creation outside the build method

To tackle the issue of creating Future objects within the build method, you can create the Future object outside the build method or set it within the initState method of a StatefulWidget.

class MyScreen extends StatefulWidget {
  ...
}

class _MyScreenState extends State<MyScreen> {
  Future _dataFuture;

  @override
  void initState() {
    super.initState();
    _dataFuture = getData();
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: _dataFuture,
      ...
    );
  }
}

2. Redraw FutureBuilder only when the state changes

Use setState() to reflect changes on the screen only when the state updates, preventing unnecessary redraws when the state remains unchanged.

3. Make use of StatefulWidget to reflect updated states

By utilizing the state updates of StatefulWidget, you can prevent unnecessary redraws. This ensures that the results of the FutureBuilder are applied to the screen only when the state changes.

By applying these solutions, you can effectively prevent unnecessary rebuilds in FutureBuilder. The next section will provide practical examples to demonstrate the application of these solutions.

Practical Application of Techniques to Avoid Unnecessary Rebuilds: A Real-Life Example

In this section, we will demonstrate how to apply the techniques discussed above to a simple real-life example.

Scenario: Fetching a List of Posts

Imagine you are developing a Flutter app that fetches a list of posts from the internet. An asynchronous task is required to fetch data, and the fetched data must be displayed on the screen. In this scenario, we will apply the techniques for avoiding unnecessary rebuilds using FutureBuilder.

1. Utilizing StatefulWidget and Shifting the Future Object Creation

First, create a StatefulWidget and initialize the app state within the initState method. Then, create the Future object within the initState method rather than the build method.

class MyApp extends StatefulWidget {
  ...
}

class _MyAppState extends State<MyApp> {
  Future _postsFuture;

  @override
  void initState() {
    super.initState();
    _postsFuture = fetchPosts();
  }

  @override
  Widget build(BuildContext context) {
    ...
  }
}

2. Effective Application of FutureBuilder

Next, use FutureBuilder to handle the asynchronous data returned by the fetchPosts() function. Use the recently created _postsFuture to reduce unnecessary redraws.

FutureBuilder(
  future: _postsFuture,
  builder: (context, snapshot) {
    if (snapshot.connectionState == ConnectionState.waiting) {
      return CircularProgressIndicator();
    } else if (snapshot.hasError) {
      return Text("Error: <${snapshot.error}>");
    } else {
      return ListView.builder(
        itemCount: snapshot.data.length,
        itemBuilder: (context, index) {
          return ListTile(title: Text(snapshot.data[index].title));
        },
      );
    }
  },
)

These modifications can effectively prevent unnecessary rebuilds, allowing your app to perform asynchronous tasks without any performance degradation.

In conclusion, to prevent unnecessary rebuilds of FutureBuilder, it is crucial to identify the root causes and apply the appropriate solutions. By doing so, you can maintain your app's performance and develop faster, more efficient apps with Flutter.